Name: Brachiosaurus‭ (‬Arm lizard‭).
Phonetic: Brak-he-o-dore-us.
Named By: Elmer S.‭ ‬Riggs‭ ‬-‭ ‬1903.
Classification: Chordata,‭ ‬Reptilia,‭ ‬Dinosauria,‭ ‬Saurischia,‭ ‬Sauropoda,‭ ‬Titanosauriformes,‭ ‬Brachiosauridae.
Species: B.‭ ‬altithorax (type).
Type: Herbivore.
Size: Up to ‬26‭ ‬meters long.
Known locations: USA,‭ ‬Morrison formation.
Time period: Kimmeridgian of the Jurassic.
Fossil representation: Several specimens,‭ ‬the most complete of which is believed to have come from a sub adult.

       The sauropod dinosaur Brachiosaurus earned its name from the fact that the arms,‭ ‬or rather the fore legs as it was quadrupedal,‭ ‬are actually longer than the hind legs.‭ ‬The fact that these are longer offers Brachiosaurus a passive advantage in reaching up into the tree canopy to feed as the neck is always arched upwards as a result.‭ ‬Since the skeleton and vertebrae would be angled in such a way,‭ ‬Brachiosaurus would not need extra powerful muscles to lift the head and neck all the way up,‭ ‬reducing the effort to feed in such a specialised way. A further adaptation were the presence of air sacs located along the neck and trunk of Brachiosaurus.‭ ‬These connected to the lungs and had the effect of lowering the body density which in turn would reduce the total weight of the neck and trunk areas.‭
       These adaptations meant that Brachiosaurus could easily live the life of a high browser feeding upon the tree canopy.‭ ‬Such specialisation also meant that Brachiosaurus would not have to compete with other herbivorous dinosaurs such as the low browsing Stegosaurus.‬Brachiosaurus could not chew its food as its jaws were only capable of opening and closing.‭ ‬Because of this it would use its spatulate‭ (‬chisel like‭) ‬teeth to crop the vegetation from the tops of trees.‭
       Its possible that Brachiosaurus was gigantothermic meaning its massive body would hold onto body heat for longer than a smaller animal.‭ ‬This would give Brachiosaurus a higher metabolism than a‭ '‬standard‭' ‬cold blooded or‭ '‬ectothermic‭' ‬animal.‭ ‬However,‭ ‬the air sacs that would have been present inside of the body may also have provided extra cooling allowing Brachiosaurus to lower its body temperature and metabolism.‭ ‬This would also reduce the required calorie intake to keep its body going,‭ ‬reducing the required amount of time for feeding.
       Fossils that were very similar to Brachiosaurus were recovered from the Tendaguru formation in Africa in‭ ‬1914.‭ ‬This new species was given the name Brachiosaurus branchai,‭ ‬but upon further study of the bones,‭ ‬several morphological differences were discovered,‭ ‬and while the new specimen was similar to B.‭ ‬altithorax,‭ ‬it was still different enough to be considered separate.‭ ‬B.‭ ‬brancai has since been renamed Giraffatitan,‭ ‬with the type species changed to G.‭ ‬brancai.
       It was once thought that Brachiosaurus had a skull like Giraffatitian,‭ ‬but when that was split off into its own group a possible key difference came to light.‭ ‬The crest forming bone that rises from the top of the skull of Giraffatitian,‭ ‬is much smaller in Brachiosaurus fossils.‭ ‬This crest was once thought to contain the nostrils but modern reconstruction places the nostrils further along the snout.‭ ‬This has led to speculation that this may have instead been a form of resonating chamber that could have been used to amplify the calls of Brachiosaurus.

Further reading
- Brachiosaurus altithorax, the largest known dinosaur. - American Journal of Science, series 4 15:299-306. - Elmer S. Riggs - 1903.
- Structure and relationships of opisthocoelian dinosaurs. Part II. The Brachiosauridae. - Geological Series (Field Columbian Museum) 2 (6): 229–247. - E. S. Riggs - 1904.
- Die Schädel der Sauropoden Brachiosaurus, Barosaurus und Dicraeosaurus aus den Tendaguru-Schichten Deutsch-Ostafrikas. - Palaeontographica (Suppl. 7) 2: 147-298. - W. Janensch - 1935/6.
- New brachiosaur material from the Late Jurassic of Utah and Colorado. - The Great Basin Naturalist 47 (4): 592–608. - J. A. Jenson - 1987.
- The brachiosaur giants of the Morrison and Tendaguru with a description of a new subgenus, Giraffatitan, and a comparison of the world's largest dinosaurs. - Hunteria 2 (3). - G. S. Paul - 1988.
- Preliminary description of a Brachiosaurus skull from Felch Quarry 1, Garden Park, Colorado, by K. Carpenter & V. Tidwell. In The Upper Jurassic Morrison Formation: An Interdisciplinary Study. Modern Geology, 23:1-4, K. Carpenter, D. Chure & J. Kirkland (eds.).
- Biostratigraphy of dinosaurs in the Upper Jurassic Morrison Formation of the Western Interior, USA, by C. E. Turner & F. Peterson. In Vertebrate Paleontology in Utah. Miscellaneous Publication 99-1. Salt Lake City, Utah: Utah Geological Survey. pp. 77–114. (David G. Gillete (ed.)). - 1999.
- Paleoecological analysis of the vertebrate fauna of the Morrison Formation (Upper Jurassic), Rocky Mountain region, U.S.A. - New Mexico Museum of Natural History and Science Bulletin, 23. Albuquerque, New Mexico: New Mexico Museum of Natural History and Science. - J. R. Foster - 2003.
- First occurrence of Brachiosaurus (Dinosauria, Sauropoda) from the Upper Jurassic Morrison Formation of Oklahoma. - PaleoBios 24 (2): 12–21. - M. F. Bonnan & M. J. Wedel - 2004.
- Brachiosaurus altithorax. - Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press. pp. 205–208. - J. Foster - 2007.
- In vitro digestibility of fern and gymnosperm foliage: implications for sauropod feeding ecology and diet selection. - Proceedings of the Royal Society B 275: 1015–1021. - J. Hummel, C. T. Gee, K.-H. Südekum, P. M. Sander, G. Nogge & M. Clauss - 2008.
- A re-evaluation of Brachiosaurus altithorax Riggs 1903 (Dinosauria, Sauropoda) and its generic separation from Giraffatitan brancai (Janensh 1914). - Journal of Vertebrate Paleontology 29 (3): 787–806. - M. P. Taylor - 2009.
- Correction: A re-evaluation of Brachiosaurus altithorax Riggs 1903 (Dinosauria, Sauropoda) and its generic separation from Giraffatitan brancai (Janensch 1914). - Journal of Vertebrate Paleontology 31 (3): 727. - M. P. Taylor - 2011.


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